@@ -323,11 +323,40 @@ pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
return get_clear_flush(mm, addr, ptep, pgsize, ncontig);
}
+/*
+ * huge_ptep_set_access_flags will update access flags (dirty, accesssed)
+ * and write permission.
+ *
+ * For a contiguous huge pte range we need to check whether or not write
+ * permission has to change only on the first pte in the set. Then for
+ * all the contiguous ptes we need to check whether or not there is a
+ * discrepancy between dirty or young.
+ */
+static int __cont_access_flags_changed(pte_t *ptep, pte_t pte, int ncontig)
+{
+ int i;
+
+ if (pte_write(pte) != pte_write(huge_ptep_get(ptep)))
+ return 1;
+
+ for (i = 0; i < ncontig; i++) {
+ pte_t orig_pte = huge_ptep_get(ptep + i);
+
+ if (pte_dirty(pte) != pte_dirty(orig_pte))
+ return 1;
+
+ if (pte_young(pte) != pte_young(orig_pte))
+ return 1;
+ }
+
+ return 0;
+}
+
int huge_ptep_set_access_flags(struct vm_area_struct *vma,
unsigned long addr, pte_t *ptep,
pte_t pte, int dirty)
{
- int ncontig, i, changed = 0;
+ int ncontig, i;
size_t pgsize = 0;
unsigned long pfn = pte_pfn(pte), dpfn;
pgprot_t hugeprot;
@@ -339,9 +368,10 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
ncontig = find_num_contig(vma->vm_mm, addr, ptep, &pgsize);
dpfn = pgsize >> PAGE_SHIFT;
+ if (!__cont_access_flags_changed(ptep, pte, ncontig))
+ return 0;
+
orig_pte = get_clear_flush(vma->vm_mm, addr, ptep, pgsize, ncontig);
- if (!pte_same(orig_pte, pte))
- changed = 1;
/* Make sure we don't lose the dirty or young state */
if (pte_dirty(orig_pte))
@@ -354,7 +384,7 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn)
set_pte_at(vma->vm_mm, addr, ptep, pfn_pte(pfn, hugeprot));
- return changed;
+ return 1;
}
void huge_ptep_set_wrprotect(struct mm_struct *mm,
For contiguous hugetlb, huge_ptep_set_access_flags performs a get_clear_flush (which then flushes the TLBs) even when no change of ptes is necessary. Unfortunately, this behaviour can lead to back-to-back page faults being generated when running with multiple threads that access the same contiguous huge page. Thread 1 | Thread 2 -----------------------------+------------------------------ hugetlb_fault | huge_ptep_set_access_flags | -> invalidate pte range | hugetlb_fault continue processing | wait for hugetlb_fault_mutex release mutex and return | huge_ptep_set_access_flags | -> invalidate pte range hugetlb_fault ... This patch changes huge_ptep_set_access_flags s.t. we first read the contiguous range of ptes (whilst preserving dirty information); the pte range is only then invalidated where necessary and this prevents further spurious page faults. Fixes: d8bdcff28764 ("arm64: hugetlb: Add break-before-make logic for contiguous entries") Reported-by: Lei Zhang <zhang.lei@jp.fujitsu.com> Signed-off-by: Steve Capper <steve.capper@arm.com> --- Changed in v2: we just check dirty, young for the contiguous range and writable for the first pte in the range. --- arch/arm64/mm/hugetlbpage.c | 38 ++++++++++++++++++++++++++++++++++---- 1 file changed, 34 insertions(+), 4 deletions(-)